1. Field of the Invention
The present invention relates to a method for operating a gas turbine, in particular in a power plant.
2. Brief Description of the Related Art
Usually gas turbines are fueled with natural gas. Natural gas is mainly comprised of CH4 (methane). Furthermore, natural gas also contains so-called non-CH4 components that can be diluting or enrichment substances. Examples of diluting substances are N2 (nitrogen) and CO2 (carbon dioxide). Enrichment substances usually are higher saturated hydrocarbons such as C2H6 (ethane), C3H8 (propane), butane, etc.
Currently it is customary to characterize the quality, i.e., the composition of natural gas, by using two indices. These are the calorific value on one hand and the Wobbe index on the other hand. Up until now it furthermore has been customary to operate gas turbines with natural gas of consistent quality.
Today gas supply companies are not yet able to guarantee consistent quality for the natural gas they supply. As part of the liberalization of the natural gas market, natural gas suppliers increasingly attempt to optimize natural gas demand and natural gas prices. The result is that natural gas is obtained from different sources, is mixed and supplied to the consumers. This in turn results in a high degree of variability of the natural gas with regard to quality and/or composition. The composition of natural gas in turn can influence the combustion process in gas turbines. The indices known up until now (calorific value and Wobbe index) are not suitable to describe these effects on the operation of gas turbines with the necessary degree of accuracy. Therefore, power plant operators must be prepared for varying natural gas quality in the future.